Cyclosporin A is a lipophilic cyclic undecapeptide of molecular weight 1203 isolated from the fungus Tolypoclodium inflatum Gams which produces calcium dependent, specific and reversible inhibition of transcription of interleukin-2 and several other cytokines, most notably in T helper lymphocytes. Because of its immunosuppressive properties, it is widely used as first line therapy in the prophylaxis and treatment of transplant rejection and various autoimmune diseases. In patients with severe disease refractory to standard treatment, oral cyclosporin is an effective therapy in acute ocular Behcet's syndrome, endogenous uveitis, psoriasis, atopic dermatitis, rheumatoid arthritis, active Crohn's disease and nephrotic syndrome. This drug has also been used to treat patients with moderate or severe aplastic anaemia who are ineligible for bone marrow transplantation and those with primary biliary cirrhosis. Cyclosporin may be effective in patients with intractable pyoderma gangrenosum, polymyositis/dermatomyositis or severe, corticosteroid-dependent asthma. Cyclosporin is known to have a very specific effect on T-cell proliferation although the precise mechanism remains unclear. It has been shown to be an effective modifier of multidrug resistance in human and rodent cells. A number of non-immunosuppressive analogties of cyclosporin A have been shown to have resistance modifier activity and some are more potent than the parent compound.
Hypertrichosis, gingival hyperplasia and neurological and gastrointestinal effects are the most common adverse events in cyclosporin recipients. Also, changes in laboratory variables indicating renal dysfunction are relatively common.
Cyclosporin is highly lipophilic, poorly water soluble and, therefore, typically supplied as an olive oil or peanut oil solution for clinical use. However, the bioavailability of cyclosporin from such oily solutions is very low and gives rise to great intersubject variation with reported systemic availability ranging from 4 to 25% (Takada, K. et al, J. Pharmacobio-Dyn., 11:80-7 (1988)). The bioavailability of cyclosporin has been reported to be dependent on food, bile and other interacting factors (Fahr, A., Clin. Pharmacokinetics, 24:472-95 (1993)). In a recent study in which a microemulsion preparation of cyclosporin was administered locally to different parts of the small and large intestine (duodenum, jejunum, ileum and colon descendens), cyclosporin was found to be absorbed predominantly in the small intestine (Drewe, J. et al., Br. J. Clin. Pharmac., 33:39-43 (1992)).
Cyclosporin A has been encapsulated in poly-D,L-lactide-co-glycolide microspheres and nanospheres (Alonso, J., Proceed. Intern. Symp. Control. Rel. Bioact. Mat., 20:109-10 (1993)). However, these microspheres and nanospheres failed to release more than 50% of the entrapped cyclosporin within a 28 day period.
Thus, to address the toxicity and intra- and intersubject variation in availability issues, there exists a need for a cyclosporin pharmaceutical formulation with increased bioavailability. Further, there exists a need for a cyclosporin formulation which efficiently targets cyclosporin to the absorption site(s) for cyclosporin.